What the Theory Says Some scientists theorize that at one time, all of the matter in the universe was condensed into one very small, very dense point called the singularity.
This singularity suddenly and violently expanded, sending matter out in all directions.
The new universe eventually cooled and the matter formed today’s galaxies.
The universe is still expanding today!

Evidence to support the Big Bang – Red Shift Over time, astronomers have discovered that the light being given off by some galaxies has shifted in color from blue to red.
This means that those galaxies are traveling further away from us and each other, further supporting the idea that the Universe is still expanding.

Weaknesses of the Theory Scientists can’t explain why the singularity exploded in the first place.
Critics say that the Big Bang Theory says that the universe was created from nothing, which violates the Law of Conservation of Mass.
The theory has a problem explaining why most of the universe has a uniform temperature.